How to dose MSU well water fertilizer
 

Good morning everyone!
I have a phalaenopsis. I recently learned about water hardness being important for learning how to fertilize orchids. I measured my tap water hardness using a titrant and got 15°f (french degress). For what I could understand it's considered hard water so I decided to ditch my current fertilizer with which I never saw results (it was 3-4-5, never really saw any growth on my orchid), and buy the MSU fertilizer for well water/hard tap water 19-4-23.

Should I just follow the instructions on the label (1 teaspoon per gallon of water) or are there better approaches? Cause I've read around things about Nitrogen being the most important to dose correctly and 125 ppm being a good amount, but to be honest my math skills are terrible and I don't really know what it means or how to measure it.

Explain like I'm five if possible, thanks a lot!

Edit: I keep my orchid in a vase full of only bark, and usually water my orchid by submerging it in another vase where I dilute the fertilizer for around 10 minutes. Felt like it was important to specify. I decide when to water it by weighing it every morning, if it's weight decreased less than 3g from the day before I water it.

oh boy, here we go again opening the can of fertilizer flame wars! so, for us we don’t really dig too deep here because even tho i have a strong background in biology and houseplants in general, i am not smart enough to do the math either. and on top of that, as you have seen, everyone’s water is different before we add any additives.

soooo, to get a baseline, if i were you i would start with 1/4 strength of the recommended dosage. follow that regimen for a year to get a sense of growth thru all seasons. other way, it’s probly better than what you were doing. 3 weeks of ferts and then a week of plain water flush.

all that said, fertilizers are useless if the roots are bad and can’t take it up. like all things sciency, a sample size of 1 is wayyy too small to reach any valid conclusions. so my first recommendation would be to get a couple more orchids and draw some comparisons from there. perhaps your orchid isn’t growing because it is on its way out, and it has nothing to do with fertilizers. just some thoughts. but listen more to the real pros here that will surely chime in. we spent all of 2022 essentially not fertilizing at all and we did get a fair amount of blooms this year. of course, we aren’t winning any awards! but honestly, the plant should at least be growing with water alone, so if it ain’t growing at all i think fertilizers and drilling down on complexities are barking up the wrong tree....best of luck with the orchid tho!!

Thanks for the long answer! My orchid is a foundling, let's call it like that. I bought it this winter from a shop that has nothing to do with plants and was keeping it outside at like 8°C on a rainy day. I basically got it home for free and tried to save it. It had one flower and I managed to get two more to bloom. When they eventually fell, I cut the stem above the top closed node and since then I feel like nothing moved. The orchid looks healthy, I actually took it out of the vase just to check the roots inside yesterday and I didn't have any rotten ones.
Started thinking about improving my fertilizing since from a previous question I got told the one I was using was weak, and here I am know trying to learn :)

I have found that applying a solution of 75-125 ppm N weekly does the trick. Pots differ in size and I know that potting media don’t retain 100% of the solution and orchid roots don’t absorb 100% of what is retained, so really have no idea how many milligrams of nutrition they are getting, but it seems to be working fine - enough to support good growth and blooming but not enough to be damaging.

There really was no need to change formula from what you had, but the MSU WW formula is a good one, so it’s no issue.

Divide 9.2 by the %N in the formula - the results are the ml of powder to add to a liter of water to be at the middle of that range, with room for rounding convenience.

Your old fertilizer was 3%N, so 9.2/3 would lead me to use 3ml/L. The MSU is 19%N, so 9.2/19=0.48, so 1/2 ml/L is fine.

Phals are OK with quite a lot of dissolved minerals in water. Your tap water is fine for them. Some other orchids need water that is more pure.

1/2 ml per liter?! get out your micropipette!!

So, I've been doing a bit of reading, since at this point I've bought the fertilizer and I might as well use it properly.

If we follow this pdf, that sounds promising, table 2, for weekly fertilizing it says to point at obtaining a Nitrogen concentration between 100 and 160 ppm.
https://staugorchidsociety.org/PDF/C...ySueBottom.pdf

Now since I'm bad at math, I found this article specific about the MSU fertilizer. At the very bottom it explains how to obtain a solution with 125ppm nitrogen.

Given that the fertilizer has 19% Nitrogen and that
I need 1.5 L that in gallons are 0.3962580785 we have:

(125*0.3962580785)/(19*1200)=0.002 pounds

that are 0.907 g

Now, is it me or a gram of fertilizer once a week sounds too little? Literally I'm lucky to have a scale that measures in milligrams, but really orchids need that little? I'm so confused.

Using info straight from the manufacturer, MSU RO requires 0.74 g/L for 100 ppm N, so that means 0.925 grams for 125 ppm N.

If you need 1.5L of solution, that would be 1.11 g or 1.3875g, respectively, so if you simply weighed out 1.25g, you’d be well within that range.

No, that is not too little for weekly feeding.

Well...two options, I keep only this orchid and the fertilizer is gonna last forever, or I buy more orchids!

I think that you have your answer. :rofl: I think that your orchid needs company...